1. Field of the Invention
The present invention relates to a heater inspection apparatus and a semiconductor manufacturing apparatus having the heater inspection apparatus thereon.
2. Description of the Related Art
Conventionally, a heater of a resistance heating type made of molybdenum disilicide whose resistance value is low at normal temperature and becomes larger in accordance with the increase in temperature has been in use in a heat treatment apparatus, as a semiconductor manufacturing apparatus, for heat-treating objects to be processed in a furnace at high temperature (See Patent Document 1, for example).
As a heater inspection apparatus of such a semiconductor manufacturing apparatus, one as described below is available.
FIG. 7 is a circuit diagram of a heater inspection apparatus as a first conventional example and a semiconductor manufacturing apparatus having the heater inspection apparatus mounted thereon.
FIG. 7 shows a commercial power source 1, a terminal block 2 for power reception, a protective breaker (NFB) 3, a power source transformer 4, a thyristor 6 for controlling heater power, a heater 7 for heating, a thermocouple 8 that measures the temperature of the heater 7, a current transformer 40 for detecting a disconnection of the heater 7, and a thermoregulator 30 that controls the temperature of the heater 7.
In controlling the temperature of the heater 7, the protective breaker 3 and the thyristor 6 are turned on while the commercial power source 1 is being supplied to the terminal block 2 for power reception, so that the commercial power source 1 is supplied to the heater 7 via the protective breaker 3 and the thyristor 6.
At this time, a current passes through the heater 7 to raise the heater temperature. The thermocouple 8 for temperature measurement converts the raised temperature of the heater 7 to an electrical signal to feed it back to the thermoregulator 30. The thermoregulator 30 computes a difference between a numerical value fed back from the thermocouple 8 and a set temperature of the heater 7 to control on/off of the thyristor 6.
The disconnection of the heater 7 can be detected by discriminating whether or not a current flows through the current transformer 40 for current detection. Specifically, it is judged that the disconnection exists when no current flowing from the current transformer 40 to the heater 7 is detected even though the thermoregulator 30 outputs to the thyristor 6 a command for power supply to the heater 7.
FIG. 8 is a circuit diagram of a heater inspection apparatus as a second conventional example and a semiconductor manufacturing apparatus having the heater inspection apparatus mounted thereon.
FIG. 8 shows, in addition to the portions shown in FIG. 7, a disconnection detector 50 that discriminates the existence of the disconnection of the heater 7. A heating method of the heater 7 is the same as that explained using FIG. 7.
In the second conventional example, in order to detect the disconnection of the heater 7, a current flowing through the current transformer 40 for current detection is measured, so that the disconnection of the heater 7 can be discriminated. Specifically, the disconnection detector 50 monitors a terminal voltage of the heater 7 that is supplied to the heater 7 and a power supplied to the heater 7 from the current transformer 40, and when a great change in a current change rate of the heater 7 is detected or when no current can be detected, even though the terminal voltage of the heater 7 exists, it is judged that the disconnection exists.
(Patent Document 1)
Japanese Patent Laid-open No. Hei 4-155828
In the conventional art, however, monitoring of a current in a heater is only possible way as a method of detecting the disconnection of the heater, and the best that can be done to replace the heater before the disconnection occurs is to make judgment based on materials of the heater and its usage environment.
The disconnection of a heater does not allow normal heat treatment in a furnace, resulting in problems such as a defective lot of objects to be processed, which gives influence to productivity. The influence is especially significant in a vertical furnace since a large number of objects to be processed are processed at a time therein. In order to compensate for this situation, spare heaters are prepared and periodical replacement is conducted. However, the life of the heater is leniently judged, and consequently, such a problem also arises that the disconnection occurs within a period of an estimated life span.